Requirements for modern internal combustion engines—both with regard to the statutory framework with respect to permissible emission values and increased expectations of end users with regard to driving comfort, engine smoothness, and low consumption—are continuously increasing.
To meet these requirements, very precise control of the fuel combustion is needed. In an internal combustion engine having a so-called common rail system fuel is pumped at high pressure into a common reservoir known as a rail via a high-pressure pump and stored in the rail. The fuel is directed from this rail to the injectors. The control parameters of the injectors needed for injection are predefined by an engine control unit as a function of the operating point. The pressure of the fuel in the rail at which the fuel is injected into the combustion chamber is a decisive and central variable for the combustion.
Common rail systems of this type have a rail pressure sensor which is an integral component of the common rail injection system. The values of this sensor are analyzed in the engine control unit and used for regulating the desired setpoint rail pressure and for ascertaining the required electrical control of the injection actuator required for a certain injected quantity, for example, of a piezoelectric injector or an injector having a solenoid valve. An unrecognized maladjustment/drift of this rail pressure sensor therefore results in an erroneous injected quantity and thus in poorer emissions. For this reason, the rail pressure sensor must be monitored due to the applicable regulations for on-board diagnosis (OBD).
Purely in principle, the sensor could be monitored by installing a second sensor. However, this is impracticable for cost reasons.